Bi-axial behaviours of abraded and rehabilitated FRP decks as anisotropic plates under concentrated wheel loading

For in-service GFRP (glass fibre-reinforced polymer) cellular bridge decks, wheel loads can induce damage of the anti-skid surfacing-to-deck bond, thereby loosening fragments of surfacing that then cause abrasion of the deck’s top flange under further wheel loads. Indeed, over the last 20 years, wheel load-induced damage to the top flanges of FRP decks on the road network has been observed in different countries, after periods in service ranging from a few days to a few years, due to inadequate design. Bonding of uni-directional GFRP panels to the abraded multi-directional flange constitutes a potentially effective rehabilitation strategy, but it also influences the deck’s local wheel-load response by altering the anisotropy of the top flange. The present paper uses an experimental-numerical study to explore this role of anisotropy for both abraded and rehabilitated decks. The experiments captured the top flanges’ peak biaxial strains, using gauges installed on the flange soffits to avoid damage by the wheels. The numerical model captures the morphology of the deck, the actual spread of the tyre load over the contact zone and spatial variations in anisotropy of the abraded or built-up flanges and of the webs. The results show that the uni-axially dominated rehabilitation strategy strongly improves bi-axial response to static wheel loads. The numerical model encouragingly predicts the bi-axial strains for each of the abraded and rehabilitated decks, and reliably predicts the strain reductions due to rehabilitation. Refined meshes along the tyre-loaded local flange span, with coarser meshes in adjacent spans, enable these reasonable predictions of response. It is concluded that top flange soffit gauges installed via ad-hoc tooling inserted through holes in the bottom flange, in tandem with rigorous numerical modelling, constitutes an effective two-pronged approach for elucidating wheel load effects

Fibre waviness in pultruded bridge deck profiles: Geometric characterisation and consequences on ultimate behaviour

Conventional tests cannot be used to establish the important influence of fibre waviness, a manufacturing legacy at the flange-web joints (FWJs) of pultruded GFRP bridge decks, on the local ultimate behaviour of such decks. Hence a novel, simple and reliable three-step experimental scheme for that purpose is presented herein, using one pultruded deck profile as an exemplar. First, the joints to be targeted for testing - namely those within the single deck unit and the hybrid joints formed by bonding deck units together - are identified. Second, an effective manual method is put forward to map this waviness at the FWJs. Third, a test is introduced which enables statically determinate loading (via an adjoining flange) of one joint at a time, while also ensuring continuity between this joint and the remaining deck so that the real load paths within the deck are preserved. During the tests failure always occurred by fracture of the wavy fibre-resin interfaces within the FWJs. In the hybrid joints, this failure occurred on the same side of the adhesive layer as the load. The strongest joint had the least waviness. For the flange-single web (but not the flange-double web) joint, bonding transformed the wavy fracture pattern and quadrupled the failure load. It is concluded that this simple test, which also reveals the influence of fibre waviness on the flange's local flexural stiffness, can be further used to characterise joint fatigue performance

Switch from connection ductility to reinforcement ductility with curvature reversal in timber-concrete composites

While multi-span continuity can be used to structurally enhance timber-concrete composites (TCCs), there has been scant research into the associated nonlinear load responses particularly of the resulting TCC zones under negative curvature. Consequently this paper presents tests to failure of TCC specimens using hardwood laminated veneer lumber joists and steel mesh connectors, one specimen (TP) under positive curvature, the other (TN) under negative curvature. It was found that the mesh connectors enabled high levels of slab-joist interaction not only in TP where the slab was almost uncracked, but also in TN where the slab exhibited pronounced cracking. Such distinct interaction enabled TN and TP to develop more than twice and six times, respectively, the stiffness of the joist acting alone. Both TCC members exhibited encouraging ductility, the source of which switched from connection yield distributed along half the span in TP to steel rebar yield concentrated at midspan in TN. TP displayed deflection (global) and curvature (local) ductility near-plateaux over ranges close to or exceeding the corresponding elastic ranges, while for TN the ductility was manifest as low tangent stiffness regimes over deflection and curvature ranges generously exceeding the corresponding elastic ranges. A conspicuous residual hinge at midspan in TN and significant residual end slip in TP provided visual evidence of the ductility. These observations address the issue of TCC connection effectiveness in cracked concrete that has emerged from updating EC5. Crucially, the ductility of TN is predicated on the hardwood’s high strain to fracture in flexure, which ensured that extensive rebar plasticity preceded failure of the timber

Characterisation of local damage in pultruded GFRP road bridge decks with random fibre mat misalignments

The extent to which random, manufacturing-induced fibre mat misalignments compromise the structural integrity of pultruded GFRP road bridge decks is not fully understood. The problem is often critical at the web-flange junctions, which frequently contain the most severe misalignments and are subjected to high moment-shear (M−V) combinations due to local tyre load effects. To that end, in the presently reported experimental study, determinate M−V combinations were applied at the junctions of a pultruded GFRP bridge deck, without artificially restraining (e.g. by clamping, which spuriously strengthens) these junctions. For any given M−V ratio, significant scatter was observed in the damage patterns and loads up to ultimate, owing to random fibre mat misalignments which have been digitally documented in a previous paper. Damage occurred mostly within the junctions, and sometimes in the adjoining flanges. Relative to misalignment-free specimens, the first fracture moments dropped by 19% and 21% for junctions containing flip and wrinkle misalignments respectively. 19% of tests showed higher tangent stiffnesses after damage, probably due to beneficial changes in load-carrying mechanism. A three-pronged approach, based on the load-response, acoustic emission and video data, enables the definition of damage indices, thereby paving the way for integrity assessment of pultruded decks under local tyre load effects

Interpretation of sensor data from in situ tests on a transversely bonded fibre-reinforced polymer road bridge

The Frampton Cotterell fibre-reinforced polymer road bridge deck comprises pultruded glass-fibre-reinforced polymer units which are laid longitudinally and are adhesively bonded transversely, in contrast to previous glass-fibre-reinforced polymer deck bridges where the pultruded units were laid transversely. This novel layout dictates that transverse distribution of live loading occurs only through the deck’s flanges and entails possible transverse tension which should be controlled to avoid cracks through the bonded deck–deck joints. This article assesses these structural actions by interpreting strains and deflections recorded during lorry testing of the bridge. Transverse distribution is evaluated by comparing transverse profiles of recorded longitudinal strains and of predicted longitudinal moments, with the conclusions qualitatively reinforced using a deflected surface based on the test recordings. Evidence of the deck acting as a continuum free of propagating joint cracks comes from the fact that the strains recorded during complementary lorry runs along the bridge satisfy the superposition principle and that the recorded strain influence lines replicate an idiosyncratic feature of the moment influence line without redistribution effects. That feature was then exploited to inform the strategy for a braking test which produced valuable vibration data for the bridge. Test data integrity is corroborated by cross checking deflections recorded from different types of sensors. It is concluded that since longitudinal placement of pultruded decks enhances the versatility of fibre-reinforced polymer bridges, this sensor layout and data interpretation process may form part of a wider strategy for health monitoring of such bridges

Relative influences of cracking and connection yield on transverse distributions of moments and reactions in timber-concrete composites

This paper uses tests backed up by nonlinear FE analysis for parametric study of transverse load sharing in large-scale timber-concrete composite (TCC) specimens, each comprising multiple hardwood LVL joists fastened to a single concrete slab via bonded-in, ductile steel mesh connectors. The study for the first time compares midspan moment sharing with support reaction sharing across the full range of behaviour up to failure for two distinct connection layouts, and it highlights the relative influences of connector yield and concrete cracking on the nonlinear load sharing characteristics. For the specific examples of this study, the results show that while cracking had little effect on transverse distribution of midspan moments, it did change the transverse distribution of support reactions by a factor of up to 1.60. Conversely, connection yield had little effect on transverse support reaction distribution, but it changed the transverse distribution of midspan moments by a factor of up to 1.62. Further, the test-verified FE analyses revealed that an inadvertent 20% drop in concrete tensile strength observed in the tests exacerbated support reaction sharing by up to 12.5%. These numbers approach or exceed the safety factors used in design. Wider studies are needed to determine practical bounds for these load sharing effects and to develop user-friendly means of allowing for these effects in design

Stochastic population growth in spatially heterogeneous environments

Classical ecological theory predicts that environmental stochasticity increases extinction risk by reducing the average per-capita growth rate of populations. To understand the interactive effects of environmental stochasticity, spatial heterogeneity, and dispersal on population growth, we study the following model for population abundances in $n$ patches: the conditional law of $X_{t+dt}$ given $X_t=x$ is such that when $dt$ is small the conditional mean of $X_{t+dt}^i-X_t^i$ is approximately $[x^i\mu_i+\sum_j(x^j D_{ji}-x^i D_{ij})]dt$, where $X_t^i$ and $\mu_i$ are the abundance and per capita growth rate in the $i$-th patch respectivly, and $D_{ij}$ is the dispersal rate from the $i$-th to the $j$-th patch, and the conditional covariance of $X_{t+dt}^i-X_t^i$ and $X_{t+dt}^j-X_t^j$ is approximately $x^i x^j \sigma_{ij}dt$. We show for such a spatially extended population that if $S_t=(X_t^1+...+X_t^n)$ is the total population abundance, then $Y_t=X_t/S_t$, the vector of patch proportions, converges in law to a random vector $Y_\infty$ as $t\to\infty$, and the stochastic growth rate $\lim_{t\to\infty}t^{-1}\log S_t$ equals the space-time average per-capita growth rate \sum_i\mu_i\E[Y_\infty^i] experienced by the population minus half of the space-time average temporal variation \E[\sum_{i,j}\sigma_{ij}Y_\infty^i Y_\infty^j] experienced by the population. We derive analytic results for the law of $Y_\infty$, find which choice of the dispersal mechanism $D$ produces an optimal stochastic growth rate for a freely dispersing population, and investigate the effect on the stochastic growth rate of constraints on dispersal rates. Our results provide fundamental insights into "ideal free" movement in the face of uncertainty, the persistence of coupled sink populations, the evolution of dispersal rates, and the single large or several small (SLOSS) debate in conservation biology.Comment: 47 pages, 4 figure

Promoting successful participation of people living with Alzheimer's disease and related dementias in pain-related neuroimaging research studies

Recruitment and retention of participants for pain-related neuroimaging research is challenging and becomes increasingly so when research participants have a diagnosis of Alzheimer's disease and related dementias (ADRD). This article shares the authors' recommendations from several years of successful recruitment and completion of pain-related neuroimaging studies of people living with ADRD and includes supportive literature. While not an exhaustive list, this review covers several topics related to recruitment and retention of participants living with ADRD, including community engagement, capacity to consent, dementia diagnostic criteria, pain medication and other study exclusion criteria, participant and caregiver burden, communication concerns, and relationships with neuroimaging facilities. Threaded throughout the paper are important cultural considerations. Additionally, we discuss implications of the coronavirus (COVID-19) pandemic for recruitment. Once tailored to specific research study protocols, these proven strategies may assist researchers with successfully recruiting and retaining participants living with ADRD for pain-related neuroimaging research studies toward improving overall health outcomes

Adaptive remodeling of the bacterial proteome by specific ribosomal modification regulates Pseudomonas infection and niche colonisation

Post-transcriptional control of protein abundance is a highly important, underexplored regulatory process by which organisms respond to their environments. Here we describe an important and previously unidentified regulatory pathway involving the ribosomal modification protein RimK, its regulator proteins RimA and RimB, and the widespread bacterial second messenger cyclic-di-GMP (cdG). Disruption of rimK affects motility and surface attachment in pathogenic and commensal Pseudomonas species, with rimK deletion significantly compromising rhizosphere colonisation by the commensal soil bacterium P. fluorescens, and plant infection by the pathogens P. syringae and P. aeruginosa. RimK functions as an ATP-dependent glutamyl ligase, adding glutamate residues to the C-terminus of ribosomal protein RpsF and inducing specific effects on both ribosome protein complement and function. Deletion of rimK in P. fluorescens leads to markedly reduced levels of multiple ribosomal proteins, and also of the key translational regulator Hfq. In turn, reduced Hfq levels induce specific downstream proteomic changes, with significant increases in multiple ABC transporters, stress response proteins and non-ribosomal peptide synthetases seen for both ΔrimK and Δhfq mutants. The activity of RimK is itself controlled by interactions with RimA, RimB and cdG. We propose that control of RimK activity represents a novel regulatory mechanism that dynamically influences interactions between bacteria and their hosts; translating environmental pressures into dynamic ribosomal changes, and consequently to an adaptive remodeling of the bacterial proteome

Dicer and miRNA in relation to clinicopathological variables in colorectal cancer patients

<p>Abstract</p> <p>Background</p> <p>Dicer is aberrantly expressed in several types of cancers. Applying real-time PCR, we detected the expression of Dicer mRNA in normal mucosa (n = 162), primary colorectal cancer (CRC) (n = 162) and liver metastasis (n = 37), and analysed the relationship between Dicer expression and clinicopathological features. We also correlated the expression of Dicer mRNA to the miRNA expression of miR-141, miR-200a, miR-200b, mir-200c and miR-429 in liver metastases.</p> <p>Methods</p> <p>RT-PCR and qPCR were used to analyse the Dicer expression in normal mucosa, primary tumour and liver metastasis by using the High Capacity cDNA Reverse Transcription Kit and TaqMan™^®Gene Expression assays for <it>Dicer </it>and <it>GAPDH</it>. RT-PCR and qPCR were used to detect miRNA expression in liver metastases by utilizing TaqMan^®MicroRNA Reverse Transcription Kit and TaqMan^®miRNA Assays. Statistical analyses were performed with STATISTICA.</p> <p>Results</p> <p>Dicer expression in rectal cancer (3.146 ± 0.953) was higher than in colon cancer (2.703 ± 1.204, P = 0.018). Furthermore the Dicer expression was increased in primary tumours (3.146 ± 0.952) in comparison to that in normal mucosa from rectal cancer patients (2.816 ± 1.009, P = 0.034) but this is not evident in colon cancer patients. Dicer expression in liver metastases was decreased in comparison to that of either normal mucosa or primary tumour in both colon and rectal cancers (P < 0.05). Patients with a high Dicer expression in normal mucosa had a worse prognosis compared to those with a low Dicer expression, independently of gender, age, tumour site, stage and differentiation (P < 0.001, RR 3.682, 95% CI 1.749 - 7.750). In liver metastases, Dicer was positively related to miR-141 (R = 0.419, P = 0.015).</p> <p>Conclusion</p> <p>Dicer is up-regulated in the early development of rectal cancers. An increased expression of Dicer mRNA in normal mucosa from CRC patients is significantly related to poor survival independently of gender, age, tumour site, stage and differentiation.</p